Vehicle control displays are either panel mounted or head mounted. Most displays are panel mounted displays (PMDs). That is, the display instrument is located on a panel in front of the operator. Head mounted displays (HMDs) are a new form of display coming into use. The unique characteristic of an HMD is that the display is attached to the head or helmet of an operator. Both PMDs and HMDs show letters, numbers, symbols, pictures and images to convey information for vehicle control to an operator. Conventional displays for land, air and sea vehicles are based on the assumption that the operator must and will direct central vision, i.e., fixate on the item or part of the display and "read" the information. For example, a driver looks at the numbers and pointer of the speedometer to see what an automobile speed is; an airplane pilot will fixate on the artificial horizon and airplane symbol to determine if the wings are level; a ship's helmsman will read the compass to check on the ship's heading.
The use of such displays and their associated symbology requires direct or almost direct fixation for legibility, and mental interpretation for meaning. This places a cognitive burden on the operator, and more importantly, when the operator is looking at the symbology, he or she is not looking for threats, obstacles or other features of the surroundings.
Conventional PMDs are viewed directly, usually at a distance of 24 or more inches from the operator. If they are too close to the eyes, it causes strain to have to focus at a near distance for prolonged periods. The symbols or pictures on an HMD always rely on an optical system to create the symbols and pictures at a distance the eye can focus on. Usually, this distance is optical infinity or very close to it; that is, everything is presented as if it were being seen from a great distance. If this were not done, the symbols and pictures would be out of focus for the eye and not readable. Also, the information being displayed is generally within the central or 30 degrees of vision, since requiring eye movement outside the central or 30 degree vision rapidly creates eye strain.
In summary, current displays for vehicle guidance have been designed and built for central vision. They must be fixated and read to obtain information. They must therefore be located or imaged at a distance that allows them to be comfortably focused on by the eye. Also, they impose a significant cognitive load on the operator, which detracts from the ability of the operator to direct attention to other tasks associated with piloting of the vehicle.
Accordingly, it would be desirable to provide a display system which is more intuitive, and reduces the cognitive and visual demand on the vehicle operator.